Fabien Potencier has made an announcement on the Symfony Blog today about all the availability of previous Symfony versions on github.

symfony1 is well and alive and many developers are now using it for projects hosted on Git. But as the official symfony 1 repository is hosted on Subversion, it's not always easy to get things versioned easily. As of today, this becomes much more easier. If you are using Git and symfony1, you can now use the official symfony1 Git clone.

There are branches for each of the major 1.x releases as well as tags for some of the minor releases. You can, of course, still access the latest packages directly via the symfony website.